Method for video coding and an apparatus

ABSTRACT

A method and apparatus are provided for encoding and decoding image information. The encoding comprises receiving a block of pixels; creating a set of motion vector prediction candidates for the block of pixels; and examining the set to determine if a motion vector prediction candidate is a temporal motion vector prediction, or a spatial motion vector prediction. If the motion vector prediction candidate is a temporal motion vector prediction, the motion vector prediction candidate is kept in the set. If the motion vector prediction candidate is a spatial motion vector prediction, it is examined whether the set comprises a motion vector prediction candidate corresponding with the spatial motion vector prediction; and if so, the motion vector prediction candidate is removed from the set. Once the set is created, one of the candidates from the set is selected to represent a motion vector prediction for the block of pixels.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/997,175, filed Jun. 4, 2018, which is a continuation of U.S.application Ser. No. 14/352,913, filed Jul. 21, 2014, which is anational phase entry of International Application No. PCT/FI2011/050926,filed Oct. 21, 2011, the entire contents of which are incorporatedherein by reference.

TECHNICAL FIELD

There is provided a method for encoding, a method for decoding, anapparatus, computer program products, an encoder and a decoder.

BACKGROUND INFORMATION

This section is intended to provide a background or context to theinvention that is recited in the claims. The description herein mayinclude concepts that could be pursued, but are not necessarily onesthat have been previously conceived or pursued. Therefore, unlessotherwise indicated herein, what is described in this section is notprior art to the description and claims in this application and is notadmitted to be prior art by inclusion in this section.

A video codec may comprise an encoder which transforms input video intoa compressed representation suitable for storage and/or transmission anda decoder that can uncompress the compressed video representation backinto a viewable form, or either one of them. The encoder may discardsome information in the original video sequence in order to representthe video in a more compact form, for example at a lower bit rate.

Many hybrid video codecs, operating for example according to theInternational Telecommunication Union's ITU-T H.263 and H.264 codingstandards, encode video information in two phases. In the first phase,pixel values in a certain picture area or “block” are predicted. Thesepixel values can be predicted, for example, by motion compensationmechanisms, which involve finding and indicating an area in one of thepreviously encoded video frames (or a later coded video frame) thatcorresponds closely to the block being coded. Additionally, pixel valuescan be predicted by spatial mechanisms which involve finding andindicating a spatial region relationship, for example by using pixelvalues around the block to be coded in a specified manner.

Prediction approaches using image information from a previous (or alater) image can also be called as Inter prediction methods, andprediction approaches using image information within the same image canalso be called as Intra prediction methods.

The second phase is one of coding the error between the predicted blockof pixels and the original block of pixels. This may be accomplished bytransforming the difference in pixel values using a specified transform.This transform may be e.g. a Discrete Cosine Transform (DCT) or avariant thereof. After transforming the difference, the transformeddifference may be quantized and entropy encoded.

By varying the fidelity of the quantization process, the encoder cancontrol the balance between the accuracy of the pixel representation,(in other words, the quality of the picture) and the size of theresulting encoded video representation (in other words, the file size ortransmission bit rate).

The decoder reconstructs the output video by applying a predictionmechanism similar to that used by the encoder in order to form apredicted representation of the pixel blocks (using the motion orspatial information created by the encoder and stored in the compressedrepresentation of the image) and prediction error decoding (the inverseoperation of the prediction error coding to recover the quantizedprediction error signal in the spatial domain).

After applying pixel prediction and error decoding processes the decodercombines the prediction and the prediction error signals (the pixelvalues) to form the output video frame.

The decoder (and encoder) may also apply additional filtering processesin order to improve the quality of the output video before passing itfor display and/or storing as a prediction reference for the forthcomingframes in the video sequence.

In some video codecs, such as High Efficiency Video Coding Working Draft4, video pictures may be divided into coding units (CU) covering thearea of a picture. A coding unit consists of one or more predictionunits (PU) defining the prediction process for the samples within thecoding unit and one or more transform units (TU) defining the predictionerror coding process for the samples in the coding unit. A coding unitmay consist of a square block of samples with a size selectable from apredefined set of possible coding unit sizes. A coding unit with themaximum allowed size can be named as a largest coding unit (LCU) and thevideo picture may be divided into non-overlapping largest coding units.A largest coding unit can further be split into a combination of smallercoding units, e.g. by recursively splitting the largest coding unit andresultant coding units. Each resulting coding unit may have at least oneprediction unit and at least one transform unit associated with it. Eachprediction unit and transform unit can further be split into smallerprediction units and transform units in order to increase granularity ofthe prediction and prediction error coding processes, respectively. Eachprediction unit may have prediction information associated with itdefining what kind of a prediction is to be applied for the pixelswithin that prediction unit (e.g. motion vector information for interpredicted prediction units and intra prediction directionalityinformation for intra predicted prediction units). Similarly, eachtransform unit may be associated with information describing theprediction error decoding process for samples within the transform unit(including e.g. discrete cosine transform (DCT) coefficientinformation). It may be signalled at coding unit level whetherprediction error coding is applied or not for each coding unit. In thecase there is no prediction error residual associated with the codingunit, it can be considered there are no transform units for the codingunit. The division of the image into coding units, and division ofcoding units into prediction units and transform units may be signalledin the bitstream allowing the decoder to reproduce the intendedstructure of these units.

In some video codecs, motion information is indicated by motion vectorsassociated with each motion compensated image block. These motionvectors represent the displacement of the image block in the picture tobe coded (in the encoder) or decoded (at the decoder) and the predictionsource block in one of the previously coded or decoded images (orpictures). In order to represent motion vectors efficiently, motionvectors may be coded differentially with respect to block specificpredicted motion vector. In some video codecs, the predicted motionvectors are created in a predefined way, for example by calculating themedian of the encoded or decoded motion vectors of the adjacent blocks.

Another way to create motion vector predictions is to generate a list ora set of candidate predictions from blocks in the current frame and/orco-located or other blocks in temporal reference pictures and signallingthe chosen candidate as the motion vector prediction. A spatial motionvector prediction is a prediction obtained only on the basis ofinformation of one or more blocks of the same frame than the currentframe whereas temporal motion vector prediction is a prediction obtainedon the basis of information of one or more blocks of a frame differentfrom the current frame. It may also be possible to obtain motion vectorpredictions by combining both spatial and temporal predictioninformation of one or more encoded blocks. These kinds of motion vectorpredictions are called as spatio-temporal motion vector predictions.

In addition to predicting the motion vector values, the reference indexin the reference picture list can be predicted. The reference index maybe predicted from blocks in the current frame and/or co-located or otherblocks in a temporal reference picture. Moreover, some high efficiencyvideo codecs employ an additional motion information coding/decodingmechanism, often called merging/merge mode, where all the motion fieldinformation, which includes motion vector and corresponding referencepicture index for each available reference picture list, is predictedand used without any modification or correction. Similarly, predictingthe motion field information is carried out using the motion fieldinformation of blocks in the current frame and/or co-located or otherblocks in temporal reference pictures and the used motion fieldinformation is signalled among a list of motion field candidate listfilled with motion field information of available blocks in the currentframe and/or co-located or other blocks in temporal reference pictures.

In some video codecs the prediction residual after motion compensationis first transformed with a transform kernel (like DCT) and then coded.The reason for this is that often there still exists some correlationamong the residual and transform can in many cases help reduce thiscorrelation and provide more efficient coding.

Some video encoders utilize Lagrangian cost functions to find optimalcoding modes, e.g. the desired Macroblock mode and associated motionvectors. This kind of cost function uses a weighting factor .lamda. totie together the (exact or estimated) image distortion due to lossycoding methods and the (exact or estimated) amount of information thatis required to represent the pixel values in an image area:

C=D+.lamda.R  (1)

where C is the Lagrangian cost to be minimized, D is the imagedistortion (e.g. Mean Squared Error) with the mode and motion vectorsconsidered, and R the number of bits needed to represent the requireddata to reconstruct the image block in the decoder (including the amountof data to represent the candidate motion vectors).

Some video codecs such as hybrid video codecs may generate a list ofmotion vector predictions (MVP) consisting of motion vectors of spatialadjacent blocks (spatial MVP) and/or motion vectors of blocks in apreviously decoded frame (temporal MVP). One of the candidate motionvectors in the list is signalled to be used as the motion vectorprediction of the current block. After the list is generated, some ofthe motion vector prediction candidates may have the same motioninformation. In this case, the identical motion vector predictioncandidates may be removed to reduce redundancy. During the decoding, ifthe temporal motion vector prediction information is unavailable due toe.g. loss of reference frame, the decoder may not know if the temporalmotion vector prediction candidate in the list is to be removed. Thismay lead to uncertainty for mapping the decoded candidate index to thecandidates whose removal decision is based on comparing motioninformation with the temporal motion vector prediction. As a result,false assignment of motion vector prediction candidates may occur whichmay lead to degradation in the picture quality and drift of false motioninformation throughout the decoding process.

SUMMARY

The present invention introduces a method for generating a motion vectorprediction list for an image block. The present invention provides videocodecs that use temporal motion vector prediction a way to decrease thedrop in picture quality when the reference temporal motion informationis unavailable. This is achieved by modifying the decisions for removingthe redundant motion vector prediction candidates from the motion vectorprediction list. The modifications may be such that the temporal motionvector prediction is not removed from the motion vector prediction listbased on a comparison with other motion vector predictions in the motionvector prediction list and other candidates are not removed from thelist based on a comparison with the temporal motion vector prediction.The reconstruction quality of the picture in cases where temporalinformation is unavailable may be improved by the described method.

According to a first aspect of the present invention there is provided amethod comprising:

receiving a block of pixels;

creating a set of motion vector prediction candidates for the block ofpixels; said creating a set comprising:

examining if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction, including the motion vector prediction candidate in the set;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, determining whether to include the motionvector prediction candidate in the set or not.

According to a second aspect of the present invention there is provideda method comprising:

receiving an encoded block of pixels;

creating a set of motion vector prediction candidates for the encodedblock of pixels; said creating a set comprising:

examining if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction, including the motion vector prediction candidate in the set;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, examining determining whether to include themotion vector prediction candidate in the set or not.

According to a third aspect of the present invention there is providedan apparatus comprising a processor and a memory including computerprogram code, the memory and the computer program code configured to,with the processor, cause the apparatus to:

receive a block of pixels;

create a set of motion vector prediction candidates for the block ofpixels; said creating a set comprising:

examine if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction, to include the motion vector prediction candidate in theset;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, to determine whether to include the motionvector prediction candidate in the set or not.

According to a fourth aspect of the present invention there is providedan apparatus comprising a processor and a memory including computerprogram code, the memory and the computer program code configured to,with the processor, cause the apparatus to:

receive an encoded block of pixels;

create a set of motion vector prediction candidates for the encodedblock of pixels; said creating a set comprising:

examine if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction, to include the motion vector prediction candidate in theset;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, to determining whether to include the motionvector prediction candidate in the set or not.

According to a fifth aspect of the present invention there is provided astorage medium having stored thereon a computer executable program codefor use by an encoder, said program code comprises instructions for:

receiving a block of pixels;

creating a set of motion vector prediction candidates for the block ofpixels; said creating a set comprising:

examining if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction or a spatio-temporal motion vector prediction, including themotion vector prediction candidate in the set;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, determining whether to include the motionvector prediction candidate in the set or not.

According to a sixth aspect of the present invention there is provided astorage medium having stored thereon a computer executable program codefor use by a decoder, said program code comprises instructions for:

receiving an encoded block of pixels;

creating a set of motion vector prediction candidates for the encodedblock of pixels; said creating a set comprising:

examining if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction, including the motion vector prediction candidate in the set;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, determining whether to include the motionvector prediction candidate in the set or not.

According to a seventh aspect of the present invention there is providedan apparatus comprising:

means for receiving a block of pixels;

means for creating a set of motion vector prediction candidates for theblock of pixels;

said means for creating a set comprising:

means for examining if a motion vector prediction candidate is atemporal motion vector prediction or a spatial motion vector prediction;

means for including the motion vector prediction candidate in the set,if the motion vector prediction candidate is a temporal motion vectorprediction;

means for determining, if the motion vector prediction candidate isbased on only a spatial motion vector prediction, whether to include themotion vector prediction candidate in the set or not.

According to an eighth aspect of the present invention there is providedan apparatus comprising:

means for receiving an encoded block of pixels;

means for creating a set of motion vector prediction candidates for theencoded block of pixels; said means for creating a set comprising:

means for examining if a motion vector prediction candidate is atemporal motion vector prediction or a spatial motion vector prediction;

means for including the motion vector prediction candidate in the set ifthe motion vector prediction candidate is a temporal motion vectorprediction;

means for determining, if the motion vector prediction candidate isbased on only a spatial motion vector prediction, whether to include themotion vector prediction candidate in the set or not.

DESCRIPTION OF THE DRAWINGS

For better understanding of the present invention, reference will now bemade by way of example to the accompanying drawings in which:

FIG. 1 shows schematically an electronic device employing someembodiments of the invention;

FIG. 2 shows schematically a user equipment suitable for employing someembodiments of the invention;

FIG. 3 further shows schematically electronic devices employingembodiments of the invention connected using wireless and wired networkconnections;

FIG. 4a shows schematically an embodiment of the invention asincorporated within an encoder;

FIG. 4b shows schematically an embodiment of a prediction reference listgeneration and modification according to some embodiments of theinvention;

FIG. 5 shows a flow diagram showing the operation of an embodiment ofthe invention with respect to the encoder as shown in FIG. 4 a;

FIG. 6a illustrates an example of spatial and temporal prediction of aprediction unit;

FIG. 6b illustrates another example of spatial and temporal predictionof a prediction unit;

FIG. 7 shows schematically an embodiment of the invention asincorporated within a decoder; and

FIG. 8 shows a flow diagram of showing the operation of an embodiment ofthe invention with respect to the decoder shown in FIG. 7.

DETAILED DESCRIPTION

The following describes in further detail suitable apparatus andpossible mechanisms for the provision of improving the predictionaccuracy and hence possibly reducing information to be transmitted invideo coding systems. In this regard reference is first made to FIG. 1which shows a schematic block diagram of an exemplary apparatus orelectronic device 50, which may incorporate a codec according to anembodiment of the invention.

The electronic device 50 may for example be a mobile terminal or userequipment of a wireless communication system. However, it would beappreciated that embodiments of the invention may be implemented withinany electronic device or apparatus which may require encoding anddecoding or encoding or decoding video images.

The apparatus 50 may comprise a housing 30 for incorporating andprotecting the device. The apparatus 50 further may comprise a display32 in the form of a liquid crystal display. In other embodiments of theinvention the display may be any suitable display technology suitable todisplay an image or video. The apparatus 50 may further comprise akeypad 34. In other embodiments of the invention any suitable data oruser interface mechanism may be employed. For example the user interfacemay be implemented as a virtual keyboard or data entry system as part ofa touch-sensitive display. The apparatus may comprise a microphone 36 orany suitable audio input which may be a digital or analogue signalinput. The apparatus 50 may further comprise an audio output devicewhich in embodiments of the invention may be any one of: an earpiece 38,speaker, or an analogue audio or digital audio output connection. Theapparatus 50 may also comprise a battery 40 (or in other embodiments ofthe invention the device may be powered by any suitable mobile energydevice such as solar cell, fuel cell or clockwork generator). Theapparatus may further comprise an infrared port 42 for short range lineof sight communication to other devices. In other embodiments theapparatus 50 may further comprise any suitable short range communicationsolution such as for example a Bluetooth wireless connection or aUSB/firewire wired connection.

The apparatus 50 may comprise a controller 56 or processor forcontrolling the apparatus 50. The controller 56 may be connected tomemory 58 which in embodiments of the invention may store both data inthe form of image and audio data and/or may also store instructions forimplementation on the controller 56. The controller 56 may further beconnected to codec circuitry 54 suitable for carrying out coding anddecoding of audio and/or video data or assisting in coding and decodingcarried out by the controller 56.

The apparatus 50 may further comprise a card reader 48 and a smart card46, for example a UICC and UICC reader for providing user informationand being suitable for providing authentication information forauthentication and authorization of the user at a network.

The apparatus 50 may comprise radio interface circuitry 52 connected tothe controller and suitable for generating wireless communicationsignals for example for communication with a cellular communicationsnetwork, a wireless communications system or a wireless local areanetwork. The apparatus 50 may further comprise an antenna 44 connectedto the radio interface circuitry 52 for transmitting radio frequencysignals generated at the radio interface circuitry 52 to otherapparatus(es) and for receiving radio frequency signals from otherapparatus(es).

In some embodiments of the invention, the apparatus 50 comprises acamera capable of recording or detecting individual frames which arethen passed to the codec 54 or controller for processing. In someembodiments of the invention, the apparatus may receive the video imagedata for processing from another device prior to transmission and/orstorage. In some embodiments of the invention, the apparatus 50 mayreceive either wirelessly or by a wired connection the image forcoding/decoding.

With respect to FIG. 3, an example of a system within which embodimentsof the present invention can be utilized is shown. The system 10comprises multiple communication devices which can communicate throughone or more networks. The system 10 may comprise any combination ofwired or wireless networks including, but not limited to a wirelesscellular telephone network (such as a GSM, UMTS, CDMA network etc.), awireless local area network (WLAN) such as defined by any of the IEEE802.x standards, a Bluetooth personal area network, an Ethernet localarea network, a token ring local area network, a wide area network, andthe Internet.

The system 10 may include both wired and wireless communication devicesor apparatus 50 suitable for implementing embodiments of the invention.

For example, the system shown in FIG. 3 shows a mobile telephone network11 and a representation of the internet 28. Connectivity to the internet28 may include, but is not limited to, long range wireless connections,short range wireless connections, and various wired connectionsincluding, but not limited to, telephone lines, cable lines, powerlines, and similar communication pathways.

The example communication devices shown in the system 10 may include,but are not limited to, an electronic device or apparatus 50, acombination of a personal digital assistant (PDA) and a mobile telephone14, a PDA 16, an integrated messaging device (IMD) 18, a desktopcomputer 20, a notebook computer 22. The apparatus 50 may be stationaryor mobile when carried by an individual who is moving. The apparatus 50may also be located in a mode of transport including, but not limitedto, a car, a truck, a taxi, a bus, a train, a boat, an airplane, abicycle, a motorcycle or any similar suitable mode of transport.

Some or further apparatuses may send and receive calls and messages andcommunicate with service providers through a wireless connection 25 to abase station 24. The base station 24 may be connected to a networkserver 26 that allows communication between the mobile telephone network11 and the internet 28. The system may include additional communicationdevices and communication devices of various types.

The communication devices may communicate using various transmissiontechnologies including, but not limited to, code division multipleaccess (CDMA), global systems for mobile communications (GSM), universalmobile telecommunications system (UMTS), time divisional multiple access(TDMA), frequency division multiple access (FDMA), transmission controlprotocol-internet protocol (TCP-IP), short messaging service (SMS),multimedia messaging service (MMS), email, instant messaging service(IMS), Bluetooth, IEEE 802.11 and any similar wireless communicationtechnology. A communications device involved in implementing variousembodiments of the present invention may communicate using various mediaincluding, but not limited to, radio, infrared, laser, cableconnections, and any suitable connection.

With respect to FIG. 4a , a block diagram of a video encoder suitablefor carrying out embodiments of the invention is shown. Furthermore,with respect to FIG. 5, the operation of the encoder exemplifyingembodiments of the invention specifically with respect to the DCprediction is shown as a flow diagram.

FIG. 4a shows the encoder as comprising a pixel predictor 302,prediction error encoder 303 and prediction error decoder 304. FIG. 4aalso shows an embodiment of the pixel predictor 302 as comprising aninter-predictor 306, an intra-predictor 308, a mode selector 310, afilter 316, and a reference frame memory 318. In this embodiment themode selector 310 comprises a block processor 381 and a cost evaluator382. The encoder may further comprise an entropy encoder 330 for entropyencoding the bit stream.

FIG. 4b depicts an embodiment of the inter predictor 306. The interpredictor 306 comprises a reference frame selector 360 for selectingreference frame or frames, a motion vector definer 361, a predictionlist modifier 363 and a motion vector selector 364. These elements orsome of them may be part of a prediction processor 362 or they may beimplemented by using other means.

The pixel predictor 302 receives the image 300 to be encoded at both theinter-predictor 306 (which determines the difference between the imageand a motion compensated reference frame 318) and the intra-predictor308 (which determines a prediction for an image block based only on thealready processed parts of current frame or picture). The output of boththe inter-predictor and the intra-predictor are passed to the modeselector 310. The intra-predictor 308 may have more than oneintra-prediction modes. Hence, each mode may perform theintra-prediction and provide the predicted signal to the mode selector310. The mode selector 310 also receives a copy of the image 300.

The mode selector 310 determines which encoding mode to use to encodethe current block. If the mode selector 310 decides to use aninter-prediction mode it will pass the output of the inter-predictor 306to the output of the mode selector 310. If the mode selector 310 decidesto use an intra-prediction mode (blocks 504-508) it will pass the outputof one of the intra-predictor modes to the output of the mode selector310.

The output of the mode selector is passed to a first summing device 321.The first summing device may subtract the pixel predictor 302 outputfrom the image 300 to produce a first prediction error signal 320 whichis input to the prediction error encoder 303.

The pixel predictor 302 further receives from a preliminaryreconstructor 339 the combination of the prediction representation ofthe image block 312 and the output 338 of the prediction error decoder304. The preliminary reconstructed image 314 may be passed to theintra-predictor 308 and to a filter 316. The filter 316 receiving thepreliminary representation may filter the preliminary representation andoutput a final reconstructed image 340 which may be saved in a referenceframe memory 318. The reference frame memory 318 may be connected to theinter-predictor 306 to be used as the reference image against which thefuture image 300 is compared in inter-prediction operations.

The operation of the pixel predictor 302 may be configured to carry outany known pixel prediction algorithm known in the art.

The pixel predictor 302 may also comprise a filter 385 to filter thepredicted values before outputting them from the pixel predictor 302.

The operation of the prediction error encoder 302 and prediction errordecoder 304 will be described hereafter in further detail. In thefollowing examples the encoder generates images in terms of 16.times.16pixel macroblocks which go to form the full image or picture. Thus, forthe following examples the pixel predictor 302 outputs a series ofpredicted macroblocks of size 16.times.16 pixels and the first summingdevice 321 outputs a series of 16.times.16 pixel residual datamacroblocks which may represent the difference between a firstmacro-block in the image 300 against a predicted macro-block (output ofpixel predictor 302). It would be appreciated that other size macroblocks may be used.

The prediction error encoder 303 comprises a transform block 342 and aquantizer 344. The transform block 342 transforms the first predictionerror signal 320 to a transform domain. The transform is, for example,the DCT transform. The quantizer 344 quantizes the transform domainsignal, e.g. the DCT coefficients, to form quantized coefficients.

The prediction error decoder 304 receives the output from the predictionerror encoder 303 and performs the opposite processes of the predictionerror encoder 303 to produce a decoded prediction error signal 338 whichwhen combined with the prediction representation of the image block 312at the second summing device 339 produces the preliminary reconstructedimage 314. The prediction error decoder may be considered to comprise adequantizer 346, which dequantizes the quantized coefficient values,e.g. DCT coefficients, to reconstruct the transform signal and aninverse transformation block 348, which performs the inversetransformation to the reconstructed transform signal wherein the outputof the inverse transformation block 348 contains reconstructed block(s).The prediction error decoder may also comprise a macroblock filter (notshown) which may filter the reconstructed macroblock according tofurther decoded information and filter parameters.

In the following the operation of an example embodiment of the interpredictor 306 will be described in more detail. The inter predictor 306receives 504 the current block for inter prediction. It is assumed thatfor the current block there already exists one or more neighboringblocks which have been encoded and motion vectors have been defined forthem. For example, the block on the left side and/or the block above thecurrent block may be such blocks. Spatial motion vector predictions forthe current block can be formed e.g. by using the motion vectors of theencoded neighboring blocks and/or of non-neighbor blocks in the sameslice or frame, using linear or non-linear functions of spatial motionvector predictions, using a combination of various spatial motion vectorpredictors with linear or non-linear operations, or by any otherappropriate means that do not make use of temporal referenceinformation. It may also be possible to obtain motion vector predictorsby combining both spatial and temporal prediction information of one ormore encoded blocks. These kinds of motion vector predictors may also becalled as spatio-temporal motion vector predictors.

Reference frames used in encoding the neighboring blocks have beenstored to the reference frame memory 404. The reference frames may beshort term references or long term references and each reference framemay have a unique index which points to the reference frame in thereference frame memory. When a reference frame is no longer used as areference frame it may be removed from the reference frame memory ormarked as a non-reference frame wherein the storage location of thatreference frame may be occupied for a new reference frame. In additionto the reference frames of the neighboring blocks the reference frameselector 360 may also select one or more other frames as potentialreference frames and store them to the reference frame memory.

Motion vector information of encoded blocks is also stored into thememory so that the inter predictor 306 is able to retrieve the motionvector information when processing motion vector candidates for thecurrent block.

In some embodiments the motion vectors are stored into one or morelists. For example, motion vectors of uni-directionally predicted frames(e.g. P-frames) may be stored to a list called as list 0. Forbi-directionally predicted frames (e.g. B-frames) there may be two lists(list 0 and list 1) and for multi-predicted frames there may be morethan two lists. Reference frame indices possibly associated with themotion vectors may also be stored in one or more lists.

In some embodiments there may be two or more motion vector predictionprocedures and each procedure may have its own candidate set creationprocess. In one procedure, only the motion vector values are used. Inanother procedure, which may be called as a Merge Mode, each candidateelement may comprise 1) The information whether ‘block was uni-predictedusing only list 0’ or ‘block was uni-predicted using only list 1’ or‘block was bi-predicted using list 0 and list 1’ 2) motion vector valuefor list 0 3) Reference picture index in list 0 4) motion vector valuefor list 1 5) Reference picture index list 1. Therefore, whenever twoprediction candidates are to be compared, not only the motion vectorvalues are compared, but also the five values mentioned above arecompared to determine whether they correspond with each other or not.

The motion vector definer 361 defines candidate motion vectors for thecurrent frame by using one or more of the motion vectors of one or moreneighbor blocks and/or other blocks of the current block in the sameframe and/or co-located blocks and/or other blocks of the current blockin one or more other frames. These candidate motion vectors can becalled as a set of candidate predictors or a predictor set. Eachcandidate predictor thus represents the motion vector of one or morealready encoded block. In some embodiments the motion vector of thecandidate predictor is set equal to the motion vector of a neighborblock for the same list if the current block and the neighbor blockrefer to the same reference frames for that list. Also for temporalprediction there may be one or more previously encoded frames whereinmotion vectors of a co-located block or other blocks in a previouslyencoded frame can be selected as candidate predictors for the currentblock. The temporal motion vector predictor candidate can be generatedby any means that make use of the frames other than the current frame.

The candidate motion vectors can also be obtained by using more than onemotion vector of one or more other blocks such as neighbor blocks of thecurrent block and/or co-located blocks in one or more other frames. Asan example, any combination of the motion vector of the block to theleft of the current block, the motion vector of the block above thecurrent block, and the motion vector of the block at the up-right cornerof the current block may be used (i.e. the block to the right of theblock above the current block). The combination may be a median of themotion vectors or calculated by using other formulas. For example, oneor more of the motion vectors to be used in the combination may bescaled by a scaling factor, an offset may be added, and/or a constantmotion vector may be added. In some embodiments the combined motionvector is based on both temporal and spatial motion vectors, e.g. themotion vector of one or more of the neighbor block or other block of thecurrent block and the motion vector of a co-located block or other blockin another frame.

If a neighbor block does not have any motion vector information adefault motion vector such as a zero motion vector may be used instead.

Creating additional or extra motion vector predictions based onpreviously added predictors may be needed when the current number ofcandidates is limited or insufficient. This kind of creating additionalcandidates can be performed by combining previous two predictions and/orprocessing one previous candidate by scaling or adding offset and/oradding a zero motion vector with various reference indices. Hence, themotion vector definer 361 may examine how many motion vector candidatescan be defined and how many potential candidate motion vectors exist forthe current block. If the number of potential motion vector candidatesis smaller than a threshold, the motion vector definer 361 may createadditional motion vector predictions.

In some embodiments the combined motion vector can be based on motionvectors in different lists. For example, one motion vector may bedefined by combining one motion vector from the list 0 and one motionvector from the list 1 e.g. when the neighboring or co-located block isa bi-directionally predicted block and there exists one motion vector inthe list 0 and one motion vector in the list 1 for the bi-directionallypredicted block.

To distinguish the current block from the encoded/decoded blocks themotion vectors of which are used as candidate motion vectors, thoseencoded/decoded blocks are also called as reference blocks in thisapplication.

In some embodiments not only the motion vector information of thereference block(s) is obtained (e.g. by copying) but also a referenceindex of the reference block in the reference picture list is copied tothe candidate list. The information whether the block was un-predictedusing only list 0 or the block was uni-predicted using only list 1 orthe block was bi-predicted using list 0 and list 1 may also be copied.The candidate list may also be called as a candidate set or a set ofmotion vector prediction candidates.

FIG. 6a illustrates an example of spatial and temporal prediction of aprediction unit. There is depicted the current block 601 in the frame600 and a neighbor block 602 which already has been encoded. The motionvector definer 361 has defined a motion vector 603 for the neighborblock 602 which points to a block 604 in the previous frame 605. Thismotion vector can be used as a potential spatial motion vectorprediction 610 for the current block. FIG. 6a depicts that a co-locatedblock 606 in the previous frame 605, i.e. the block at the same locationthan the current block but in the previous frame, has a motion vector607 pointing to a block 609 in another frame 608. This motion vector 607can be used as a potential temporal motion vector prediction-611 for thecurrent frame.

FIG. 6b illustrates another example of spatial and temporal predictionof a prediction unit. In this example the block 606 of the previousframe 605 uses bi-directional prediction based on the block 609 of theframe preceding the frame 605 and on the block 612 succeeding thecurrent frame 600. The temporal motion vector prediction for the currentblock 601 may be formed by using both the motion vectors 607, 614 oreither of them.

The operation of the prediction list modifier 363 will now be describedin more detail with reference to the flow diagram of FIG. 5. Theprediction list modifier 363 initializes a motion vector prediction listto default values in block 500. The prediction list modifier 363 mayalso initialize a list index to an initial value such as zero. Then, inblock 502 the prediction list modifier checks whether there are anymotion vector candidates to process. If there is at least one motionvector candidate in the predictor set for processing, the predictionlist modifier 363 generates 504 the next motion vector candidate whichmay be a temporal motion vector or a spatial motion vector. If theprediction list modifier determined in block 502 that there are nomotion vector candidates left, the modification of the motion vectorprediction list may be ended 506. From block 504 the process continuesin block 508. The prediction list modifier 363 examines whether thecurrent motion vector prediction is a temporal motion vector predictionor not. If it is a temporal motion vector prediction the motion vectorprediction is inserted 510 to the prediction list and no comparison thatuses temporal data with previously added motion vector predictions isperformed. The added motion vector prediction may be accompanied withthe list index and the list index may be incremented by one or by someother constant so that the list index indicates the next position in themotion vector prediction list. If the current motion vector predictionis not a temporal motion vector prediction and does not contain anymotion vector information which is based on temporal data the predictionlist modifier 363 compares 512 the motion vector of the current motionvector prediction with the motion vector info of the motion vectorpredictions in the list. Such motion vector predictions which containtemporal motion vector prediction info are excluded from the comparison.Some other spatial motion vector predictors may be excluded as well fordifferent reasons such as for reducing complexity. In other words, thosemotion vector predictions in which motion vector information containstemporal information are not taken into the comparison although themotion vector prediction were partly based on spatial motion vectors.Such situations may occur e.g. when a motion vector prediction iscombined from temporal and spatial motion vectors.

The comparison can be an identicality/equivalence check or comparing the(absolute) difference against a threshold or any other similaritymetric.

If similar spatial motion vector info is found from the list, thecurrent motion vector prediction is not added to the list. The addedmotion vector prediction may be accompanied with the list index and thelist index may be incremented by one or by some other constant so thatthe list index indicates the next position in the motion vectorprediction list. Then the process returns to block 502 to check, if thiswas the last candidate motion vector prediction to process. Otherwise,the current motion vector prediction is added 510 to the list and theprocess returns to block 502. Hence, when duplicate spatial motionvector predictions exist, the spatial motion vector prediction which hasthe smallest index in the list may be maintained in the list (theearliest occurrence of such spatial motion vector prediction in the listconstruction process) and duplicate spatial motion vector predictionshaving higher indices are not added to the list.

During the process of removal of redundant candidates, comparisonbetween motion vector predictor candidates can be based on any otherinformation than the motion vector values. For example, it can be basedon linear or non-linear functions of motion vector values, coding orprediction types of the blocks used to obtain the motion information,block size, the spatial location in the frame/(largest) codingunit/macroblock, the information whether blocks share the same motionwith a block, the information whether blocks are in the samecoding/prediction unit, etc.

As can be determined from the above the method does not includeduplicate motion vector info for spatial motion vector predictions anddoes not remove duplicate motion vector info for temporal motion vectorpredictions if such exist in the motion vector prediction candidates.

There may also be more than one temporal motion vector predictors in themotion vector predictor candidate list. In this case, all the temporalmotion vector predictors are retained in the list. Moreover, during theremoving redundant spatial motion vector predictor process, none of thetemporal motion vector predictors are used.

An example description of the invention for constructing mergingcandidate list is as follows. A1, if available; B1, if available; B0, ifavailable; A0, if available; B2, if available; Co1. A1, B1, B0, A0, B2and Co1 correspond to whole motion field information (comprising 1) Theinformation whether ‘block was uni-predicted using only list 0’ or‘block was uni-predicted using only list 1’ or ‘block was bi-predictedusing list 0 and list 1’ 2) motion vector value for list 0 3) Referencepicture index in list 0 4) motion vector value for list 1 5) Referencepicture index list 1) for different blocks. A1 corresponds to thebottom-most block on the left side of the current block, A0 correspondsto the block below the A1 block, B1 corresponds to the right-most blockabove the current block, B0 corresponds to the block on the right sideof the B1 block, B2 corresponds to the block on the top-left corner ofthe current block, and Co1 corresponds to the bottom-right corner orcentral co-located block of the current block in another frame. Themerging candidate list may be merged by removing candidates which havethe same motion vectors and the same reference indices except themerging candidate which has the smallest order in the merging candidatelist and except the Co1 merging candidate.

In some situations a temporal motion vector predictor may be removedfrom the candidate list based on information that is available even ifthe reference frame needed to generate the temporal motion vectorpredictor is unavailable.

In some embodiments the location of the temporal motion vector predictorin the motion vector predictor candidate list can be adjusted to any ofthe places. For example, the temporal motion vector predictor can alwaysbe the top or the last element in the motion vector predictor candidatelist.

For the motion vector predictor candidate list generation process, eachlist candidate can include more information than the motion vectorvalue, such as the reference lists used, the reference frames used ineach list and motion vector for each list.

During the creation of a new motion vector predictor candidate, ifinformation related to the temporal motion vector predictor may be used,the creation of motion vector predictor candidate can be modified suchthat the information related to the temporal motion vector predictor isdiscarded.

During the creation of a new motion vector predictor candidate, ifinformation related to the temporal motion vector predictor is used, thenew candidate can be discarded.

When all motion vector candidates have been examined, one motion vectoris selected to be used as the motion vector for the current block. Themotion vector selector 364 may examine different motion vectors in thelist and determine which motion vector provides the most efficientencoding result, or the selection of the motion vector may be based onto other criteria as well. Information of the selected motion vector isprovided for the mode selector for encoding and transmission to thedecoder or for storage when the mode selector determines to use interprediction for the current block. The information may include the indexof the motion vector in the list, and/or motion vector parameters orother appropriate information.

The selected motion vector and the block relating to the motion vectoris used to generate the prediction representation of the image block 312which is provided as the output of the mode selector. The output may beused by the first summing device 321 to produce the first predictionerror signal 320, as was described above.

The selected motion vector predictor candidate can be modified by addinga motion vector difference or can be used directly as the motion vectorof the block. Moreover, after the motion compensation is performed byusing the selected motion vector predictor candidate, the residualsignal of the block can be transform coded or skipped to be coded.

Although the embodiments above have been described with respect to thesize of the macroblock being 16.times.16 pixels, it would be appreciatedthat the methods and apparatus described may be configured to handlemacroblocks of different pixel sizes.

In the following the operation of an example embodiment of the decoder600 is depicted in more detail with reference to FIG. 7.

At the decoder side similar operations are performed to reconstruct theimage blocks. FIG. 7 shows a block diagram of a video decoder 700suitable for employing embodiments of the invention and FIG. 8 shows aflow diagram of an example of a method in the video decoder. Thebitstream to be decoded may be received from the encoder, from a networkelement, from a storage medium or from another source. The decoder isaware of the structure of the bitstream so that it can determine themeaning of the entropy coded codewords and may decode the bitstream byan entropy decoder 701 which performs entropy decoding on the receivedsignal. The entropy decoder thus performs the inverse operation to theentropy encoder 330 of the encoder described above. The entropy decoder701 outputs the results of the entropy decoding to a prediction errordecoder 702 and a pixel predictor 704.

In some embodiments the entropy coding may not be used but anotherchannel encoding may be in use, or the encoded bitstream may be providedto the decoder 700 without channel encoding. The decoder 700 maycomprise a corresponding channel decoder to obtain the encoded codewordsfrom the received signal.

The pixel predictor 704 receives the output of the entropy decoder 701.The output of the entropy decoder 701 may include an indication on theprediction mode used in encoding the current block. A predictor selector714 within the pixel predictor 704 determines that an intra-predictionor an inter-prediction is to be carried out. The predictor selector 714may furthermore output a predicted representation of an image block 716to a first combiner 713. The predicted representation of the image block716 is used in conjunction with the reconstructed prediction errorsignal 712 to generate a preliminary reconstructed image 718. Thepreliminary reconstructed image 718 may be used in the predictor 714 ormay be passed to a filter 720. The filter 720, if used, applies afiltering which outputs a final reconstructed signal 722. The finalreconstructed signal 722 may be stored in a reference frame memory 724,the reference frame memory 724 further being connected to the predictor714 for prediction operations.

Also the prediction error decoder 702 receives the output of the entropydecoder 701. A dequantizer 792 of the prediction error decoder 702 maydequantize the output of the entropy decoder 701 and the inversetransform block 793 may perform an inverse transform operation to thedequantized signal output by the dequantizer 792. The output of theentropy decoder 701 may also indicate that prediction error signal isnot to be applied and in this case the prediction error decoder producesan all zero output signal.

The decoder selects the 16.times.16 pixel residual macroblock toreconstruct. This residual macroblock is also called as a current block.

The decoder may receive information on the encoding mode used inencoding of the current block. The indication is decoded, whennecessary, and provided to the reconstruction processor 791 of theprediction selector 714. The reconstruction processor 791 examines theindication and selects one of the intra-prediction, if the indicationindicates that the block has been encoded using intra-prediction, or theinter-prediction mode, if the indication indicates that the block hasbeen encoded using inter-prediction.

For inter-prediction mode(s) the reconstruction processor 791 maycomprise one or more elements corresponding to the prediction processor362 of the encoder, such as a motion vector definer, a prediction listmodifier and/or a motion vector selector.

The reconstruction processor 791 initializes a motion vector predictionlist to default values in block 800. Then, in block 802 thereconstruction processor 791 checks whether there are any motion vectorcandidates to process. If there is at least one motion vector candidatein the predictor set for processing, the reconstruction processor 791generates 804 the next motion vector candidate which may be a temporalmotion vector or a spatial motion vector. If the reconstructionprocessor 791 determined in block 802 that there are no motion vectorcandidates left, the modification of the motion vector prediction listmay be ended 806. From block 804 the process continues in block 808. Thereconstruction processor 791 examines whether the current motion vectorprediction is a temporal motion vector prediction or not. If it is atemporal motion vector prediction the motion vector prediction isinserted 810 to the prediction list. As was the case in the encoder,such motion vector predictions which contain temporal motion vectorprediction info are excluded from the comparison and are added to thelist by the reconstruction processor 791. If the current motion vectorprediction is not a temporal motion vector prediction the reconstructionprocessor 791 compares 812 the motion vector of the current motionvector prediction with the motion vector info of the motion vectorpredictions in the motion vector prediction list. If similar motionvector info is found from the list, the current motion vector predictionis not added to the list and the process returns to block 802 to check,if this was the last motion vector prediction to process. Otherwise, thecurrent motion vector prediction is added 810 to the list and theprocess returns to block 802.

When the list has been constructed the decoder may use the indication ofthe motion vector received from the encoder to select the motion vectorfor decoding the current block. The indication may be, for example, anindex to the list.

Basically, after the reconstruction processor 791 has constructed themotion vector prediction list, it would correspond with the motionvector prediction list constructed by the encoder if the reconstructionprocessor 791 has the same information available than the encoder had.If some information has been lost during transmission the informationfrom the encoder to the decoder, it may affect the generation of themotion vector prediction list in the decoder 700. However, because thetemporal motion vector predictions are maintained in the list theprobabilities that the decoder 700 is able to correctly construct themotion vector prediction list may be higher compared to the situationthat all duplicate motion vector predictions were removed.

The embodiments of the invention described above describe the codec interms of separate encoder and decoder apparatus in order to assist theunderstanding of the processes involved. However, it would beappreciated that the apparatus, structures and operations may beimplemented as a single encoder-decoder apparatus/structure/operation.Furthermore in some embodiments of the invention the coder and decodermay share some or all common elements.

Although the above examples describe embodiments of the inventionoperating within a codec within an electronic device, it would beappreciated that the invention as described below may be implemented aspart of any video codec. Thus, for example, embodiments of the inventionmay be implemented in a video codec which may implement video codingover fixed or wired communication paths.

Thus, user equipment may comprise a video codec such as those describedin embodiments of the invention above.

It shall be appreciated that the term user equipment is intended tocover any suitable type of wireless user equipment, such as mobiletelephones, portable data processing devices or portable web browsers.

Furthermore elements of a public land mobile network (PLMN) may alsocomprise video codecs as described above.

In general, the various embodiments of the invention may be implementedin hardware or special purpose circuits, software, logic or anycombination thereof. For example, some aspects may be implemented inhardware, while other aspects may be implemented in firmware or softwarewhich may be executed by a controller, microprocessor or other computingdevice, although the invention is not limited thereto. While variousaspects of the invention may be illustrated and described as blockdiagrams, flow charts, or using some other pictorial representation, itis well understood that these blocks, apparatus, systems, techniques ormethods described herein may be implemented in, as non-limitingexamples, hardware, software, firmware, special purpose circuits orlogic, general purpose hardware or controller or other computingdevices, or some combination thereof.

The embodiments of this invention may be implemented by computersoftware executable by a data processor of the mobile device, such as inthe processor entity, or by hardware, or by a combination of softwareand hardware. Further in this regard it should be noted that any blocksof the logic flow as in the Figures may represent program steps, orinterconnected logic circuits, blocks and functions, or a combination ofprogram steps and logic circuits, blocks and functions. The software maybe stored on such physical media as memory chips, or memory blocksimplemented within the processor, magnetic media such as hard disk orfloppy disks, and optical media such as for example DVD and the datavariants thereof, CD.

The memory may be of any type suitable to the local technicalenvironment and may be implemented using any suitable data storagetechnology, such as semiconductor-based memory devices, magnetic memorydevices and systems, optical memory devices and systems, fixed memoryand removable memory. The data processors may be of any type suitable tothe local technical environment, and may include one or more of generalpurpose computers, special purpose computers, microprocessors, digitalsignal processors (DSPs) and processors based on multi-core processorarchitecture, as non-limiting examples.

Embodiments of the inventions may be practiced in various componentssuch as integrated circuit modules. The design of integrated circuits isby and large a highly automated process. Complex and powerful softwaretools are available for converting a logic level design into asemiconductor circuit design ready to be etched and formed on asemiconductor substrate.

Programs, such as those provided by Synopsys, Inc. of Mountain View,Calif. and Cadence Design, of San Jose, Calif. automatically routeconductors and locate components on a semiconductor chip using wellestablished rules of design as well as libraries of pre-stored designmodules. Once the design for a semiconductor circuit has been completed,the resultant design, in a standardized electronic format (e.g., Opus,GDSII, or the like) may be transmitted to a semiconductor fabricationfacility or “fab” for fabrication.

The foregoing description has provided by way of exemplary andnon-limiting examples a full and informative description of theexemplary embodiment of this invention. However, various modificationsand adaptations may become apparent to those skilled in the relevantarts in view of the foregoing description, when read in conjunction withthe accompanying drawings and the appended claims. However, all such andsimilar modifications of the teachings of this invention will still fallwithin the scope of this invention.

In the following some examples will be provided.

In some embodiments a method comprises:

receiving a block of pixels;

creating a set of motion vector prediction candidates for the block ofpixels; said creating a set comprising:

examining if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction, including the motion vector prediction candidate in the set;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, determining whether to include the motionvector prediction candidate in the set or not.

In some embodiments a method comprises:

receiving a block of pixels; creating a set of motion vector predictioncandidates for the block of pixels; said creating a set comprising:

examining if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction or aspatio-temporal motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction or a spatio-temporal motion vector prediction, including themotion vector prediction candidate in the set;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, determining whether to include the motionvector prediction candidate in the set or not.

In some embodiments a method comprises:

receiving an encoded block of pixels;

creating a set of motion vector prediction candidates for the encodedblock of pixels; said creating a set comprising:

examining if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction, including the motion vector prediction in the set;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, determining whether to include the motionvector prediction candidate in the set or not.

In some embodiments a method comprises:

receiving an encoded block of pixels;

creating a set of motion vector prediction candidates for the encodedblock of pixels; said creating a set comprising:

examining if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction or aspatio-temporal motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction or a spatio-temporal motion vector prediction, including themotion vector prediction in the set;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, determining whether to include the motionvector prediction candidate in the set or not.

In some embodiments an apparatus comprises a processor and a memoryincluding computer program code, the memory and the computer programcode configured to, with the processor, cause the apparatus to:

receiving a block of pixels;

creating a set of motion vector prediction candidates for the block ofpixels; said creating a set comprising:

examining if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction, including the motion vector prediction in the set;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, determining whether to include the motionvector prediction candidate in the set or not.

In some embodiments an apparatus comprises a processor and a memoryincluding computer program code, the memory and the computer programcode configured to, with the processor, cause the apparatus to:

receiving a block of pixels;

creating a set of motion vector prediction candidates for the block ofpixels; said creating a set comprising:

examining if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction or aspatio-temporal motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction or a spatio-temporal motion vector prediction, including themotion vector prediction in the set;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, determining whether to include the motionvector prediction candidate in the set or not.

In some embodiments an apparatus comprises a processor and a memoryincluding computer program code, the memory and the computer programcode configured to, with the processor, cause the apparatus:

receive an encoded block of pixels;

create a set of motion vector prediction candidates for the encodedblock of pixels; said creating a set comprising:

examine if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction, to include the motion vector prediction in the set;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, to determine whether to include the motionvector prediction candidate in the set or not.

In some embodiments an apparatus comprises a processor and a memoryincluding computer program code, the memory and the computer programcode configured to, with the processor, cause the apparatus:

receive an encoded block of pixels;

create a set of motion vector prediction candidates for the encodedblock of pixels; said creating a set comprising:

examine if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction or aspatio-temporal motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction or a spatio-temporal motion vector prediction, to include themotion vector prediction in the set;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, to determine whether to include the motionvector prediction candidate in the set or not.

In some embodiments a storage medium having stored thereon a computerprogram code a computer executable program code for use by an encoder,said program codes comprise instructions for use by an encoder, saidprogram code comprises instructions for:

receiving a block of pixels;

creating a set of motion vector prediction candidates for the block ofpixels; said creating a set comprising:

examining if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction, including the motion vector prediction in the set;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, determining whether to include the motionvector prediction candidate in the set or not.

In some embodiments a storage medium having stored thereon a computerprogram code a computer executable program code for use by an encoder,said program codes comprise instructions for use by an encoder, saidprogram code comprises instructions for:

receiving a block of pixels;

creating a set of motion vector prediction candidates for the block ofpixels; said creating a set comprising:

examining if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction or aspatio-temporal motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction or a spatio-temporal motion vector prediction, including themotion vector prediction in the set;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, determining whether to include the motionvector prediction candidate in the set or not.

In some embodiments a storage medium having stored thereon a computerprogram code a computer executable program code for use by an encoder,said program codes comprise instructions for use by an encoder, saidprogram code comprises instructions for:

receiving an encoded block of pixels;

creating a set of motion vector prediction candidates for the encodedblock of pixels; said creating a set comprising:

examining if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction or a spatio-temporal motion vector prediction, including themotion vector prediction in the set;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, determining whether to include the motionvector prediction candidate in the set or not.

In some embodiments a storage medium having stored thereon a computerprogram code a computer executable program code for use by an encoder,said program codes comprise instructions for use by an encoder, saidprogram code comprises instructions for:

receiving an encoded block of pixels;

creating a set of motion vector prediction candidates for the encodedblock of pixels; said creating a set comprising:

examining if a motion vector prediction candidate is a temporal motionvector prediction or a spatial motion vector prediction or aspatio-temporal motion vector prediction;

if the motion vector prediction candidate is a temporal motion vectorprediction or a spatio-temporal motion vector prediction or aspatio-temporal motion vector prediction, including the motion vectorprediction in the set;

if the motion vector prediction candidate is based on only a spatialmotion vector prediction, determining whether to include the motionvector prediction candidate in the set or not.

In some embodiments an apparatus comprises:

means for receiving a block of pixels;

means for creating a set of motion vector prediction candidates for theblock of pixels;

said means for creating a set comprising:

means for examining if a motion vector prediction candidate is atemporal motion vector prediction or a spatial motion vector prediction;

means for including the motion vector prediction in the set, if themotion vector prediction candidate is a temporal motion vectorprediction;

means for determining, if the motion vector prediction candidate isbased on only a spatial motion vector prediction, whether to include themotion vector prediction candidate in the set or not.

In some embodiments an apparatus comprises:

means for receiving a block of pixels;

means for creating a set of motion vector prediction candidates for theblock of pixels;

said means for creating a set comprising:

means for examining if a motion vector prediction candidate is atemporal motion vector prediction or a spatial motion vector predictionor a spatio-temporal motion vector prediction;

means for including the motion vector prediction in the set, if themotion vector prediction candidate is a temporal motion vectorprediction or a spatio-temporal motion vector prediction;

means for determining, if the motion vector prediction candidate isbased on only a spatial motion vector prediction, whether to include themotion vector prediction candidate in the set or not.

In some embodiments an apparatus comprises:

means for receiving an encoded block of pixels;

means for creating a set of motion vector prediction candidates for theencoded block of pixels; said means for creating a set comprising:

means for examining if a motion vector prediction candidate is atemporal motion vector prediction, a spatial motion vector prediction ora spatio-temporal motion vector prediction;

means for including the motion vector prediction in the set if themotion vector prediction candidate is a temporal motion vectorprediction or a spatio-temporal motion vector prediction;

means for determining, if the motion vector prediction candidate isbased on only a spatial motion vector prediction, whether to include themotion vector prediction candidate in the set or not.

In some embodiments an apparatus comprises:

means for receiving an encoded block of pixels;

means for creating a set of motion vector prediction candidates for theencoded block of pixels; said means for creating a set comprising:

means for examining if a motion vector prediction candidate is atemporal motion vector prediction, a spatial motion vector prediction ora spatio-temporal motion vector prediction;

means for including the motion vector prediction in the set if themotion vector prediction candidate is a temporal motion vectorprediction or a spatio-temporal motion vector prediction;

means for determining, if the motion vector prediction candidate isbased on only a spatial motion vector prediction, whether to include themotion vector prediction candidate in the set or not.

1. A method for encoding an image, the method comprising: creating a set of motion vector prediction candidates for a block of pixels, said creating the set comprising: if a motion vector prediction candidate is based on a spatial motion vector prediction, comparing the motion vector prediction candidate to at least one spatial motion vector already included in the set, and adding the motion vector prediction candidate to the set when the motion vector prediction candidate is not equal to the at least one spatial motion vector already included in the set; and if the motion vector prediction candidate is a temporal motion vector prediction, adding the motion vector prediction candidate to the set without comparing the motion vector prediction candidate with other motion vector prediction candidates already included in the set; and selecting one motion vector prediction candidate from the set to represent a motion vector prediction for the block of pixels.
 2. The method according to claim 1, wherein said comparing comprises at least one of the following: comparing a reference index of the motion vector prediction candidate with a reference index of the at least one spatial motion vector already included in the set; and examining whether the motion vector prediction candidate is generated by processing one or more than one motion vector prediction candidates or not.
 3. The method according to claim 1, further comprising: creating an additional motion vector prediction candidate based on one or more previously added motion vector predictors in the set.
 4. The method according to claim 1, wherein each motion vector prediction candidate is associated with an index in the set, and if a motion vector prediction candidate is determined to be removed due to motion vector information corresponding with another motion vector prediction candidate, the method further comprising: examining the index of the motion vector prediction candidate and the index of the another motion vector prediction candidate, and removing the motion vector prediction candidate which has greater index.
 5. The method according to claim 1, wherein the temporal motion vector prediction is based on motion vectors of co-located blocks of a current frame and a previously encoded frame.
 6. A method for decoding an encoded image, the method comprising: creating a set of motion vector prediction candidates for a block of pixels, said creating the set comprising: if a motion vector prediction candidate is based on a spatial motion vector prediction, comparing the motion vector prediction candidate to at least one spatial motion vector already included in the set, and adding the motion vector prediction candidate to the set when the motion vector prediction candidate is not equal to the at least one spatial motion vector already included in the set; and if the motion vector prediction candidate is a temporal motion vector prediction, adding the motion vector prediction candidate to the set without comparing the motion vector prediction candidate with other motion vector prediction candidates already included in the set; and selecting one motion vector prediction candidate from the set to represent a motion vector prediction for the block of pixels.
 7. The method according to claim 6, wherein said comparing comprises at least one of the following: comparing a reference index of the motion vector prediction candidate with a reference index of the at least one spatial motion vector already included in the set; and examining whether the motion vector prediction candidate is generated by processing one or more than one motion vector prediction candidates or not.
 8. The method according to claim 6, further comprising: creating an additional motion vector prediction candidate based on one or more previously added motion vector predictors in the set.
 9. The method according to claim 6, wherein each motion vector prediction candidate is associated with an index in the set, and if a motion vector prediction candidate is determined to be removed due to motion vector information corresponding with another motion vector prediction candidate, the method further comprising: examining the index of the motion vector prediction candidate and the index of the another motion vector prediction candidate, and removing the motion vector prediction candidate which has greater index.
 10. The method according to claim 6, wherein the temporal motion vector prediction is based on motion vectors of co-located blocks of a current frame and a previously encoded frame.
 11. An apparatus embodied by a codec for encoding an image, the apparatus comprising: a processor and a memory including computer program code, the memory and the computer program code configured to, with the processor, cause the apparatus to: create a set of motion vector prediction candidates for a block of pixels, wherein the memory and the computer program code configured to, with the processor, create the set cause the apparatus to: if a motion vector prediction candidate is based on a spatial motion vector prediction, compare the motion vector prediction candidate to at least one spatial motion vector already included in the set, and add the motion vector prediction candidate to the set when the motion vector prediction candidate is not equal to the at least one spatial motion vector already included in the set; and if the motion vector prediction candidate is a temporal motion vector prediction, add the motion vector prediction candidate to the set without comparing the motion vector prediction candidate with other motion vector prediction candidates already included in the set; and select one motion vector prediction candidate from the set to represent a motion vector prediction for the block of pixels.
 12. The apparatus according to claim 11, wherein the temporal motion vector prediction is at least partly based on one or more encoded blocks in a frame different from the frame of the block of pixels and the spatial motion vector prediction is only based on one or more encoded blocks in the same frame as the frame of the block of pixels.
 13. The apparatus according to claim 11, wherein the computer program code to compare the motion vector prediction candidate to at least one spatial motion vector already included in the set cause apparatus to perform at least one of the following: compare a reference index of the motion vector prediction candidate with a reference index of the at least one spatial motion vector already included in the set; and examine whether the motion vector prediction candidate is generated by processing one or more than one motion vector prediction candidates or not.
 14. The apparatus according to claim 11, comprising further computer program code configured to, with the processor, cause the apparatus to create an additional motion vector prediction candidate based on one or more previously added motion vector predictors in the set.
 15. The apparatus according to claim 11, wherein each motion vector prediction candidate is associated with an index in the set, and if a motion vector prediction candidate is determined to be removed due to motion vector information corresponding with another motion vector prediction candidate, the apparatus further comprises computer program code configured to, with the processor, cause the apparatus to examine the index of the motion vector prediction candidate and the index of the another motion vector prediction candidate, and remove the motion vector prediction candidate which has greater index.
 16. The apparatus according to claim 11, wherein the temporal motion vector prediction is based on motion vectors of co-located blocks of a current frame and a previously encoded frame.
 17. An apparatus embodied by a codec for decoding an encoded image, the apparatus comprising: a processor and a memory including computer program code, the memory and the computer program code configured to, with the processor, cause the apparatus to: create a set of motion vector prediction candidates for an encoded block of pixels, wherein the memory and the computer program code configured to, with the processor, create the set cause the apparatus to: if a motion vector prediction candidate is based on a spatial motion vector prediction, compare the motion vector prediction candidate to at least one spatial motion vector already included in the set, and add the motion vector prediction candidate to the set when the motion vector prediction candidate is not equal to the at least one spatial motion vector already included in the set; and if the motion vector prediction candidate is a temporal motion vector prediction, add the motion vector prediction candidate to the set without comparing the motion vector prediction candidate with other motion vector prediction candidates already included in the set; and select one motion vector prediction candidate from the set to represent a motion vector prediction for the block of pixels.
 18. The apparatus according to claim 17, wherein the temporal motion vector prediction is at least partly based on one or more encoded blocks in a frame different from the frame of the block of pixels and the spatial motion vector prediction is only based on one or more encoded blocks in the same frame as the frame of the block of pixels.
 19. The apparatus according to claim 17, wherein the computer program code to compare the motion vector prediction candidate to at least one spatial motion vector already included in the set cause apparatus to perform at least one of the following: compare a reference index of the motion vector prediction candidate with a reference index of the at least one spatial motion vector already included in the set; and examine whether the motion vector prediction candidate is generated by processing one or more than one motion vector prediction candidates or not.
 20. The apparatus according to claim 17, comprising further computer program code configured to, with the processor, cause the apparatus to create an additional motion vector prediction candidate based on one or more previously added motion vector predictors in the set.
 21. The apparatus according to claim 17, wherein each motion vector prediction candidate is associated with an index in the set, and if a motion vector prediction candidate is determined to be removed due to motion vector information corresponding with another motion vector prediction candidate, the apparatus further comprises computer program code configured to, with the processor, cause the apparatus to examine the index of the motion vector prediction candidate and the index of the another motion vector prediction candidate, and remove the motion vector prediction candidate which has greater index.
 22. The apparatus according to claim 17, wherein the temporal motion vector prediction is based on motion vectors of co-located blocks of a current frame and a previously encoded frame.
 23. A non-transitory machine-readable medium having instructions stored therein, which when executed by a processor of a codec, cause the processor to perform a method for decoding an encoded image, the method comprising: creating a set of motion vector prediction candidates for a block of pixels, said creating the set comprising: if a motion vector prediction candidate is based on a spatial motion vector prediction, comparing the motion vector prediction candidate to at least one spatial motion vector already included in the set, and adding the motion vector prediction candidate to the set when the motion vector prediction candidate is not equal to the at least one spatial motion vector already included in the set; and if the motion vector prediction candidate is a temporal motion vector prediction, adding the motion vector prediction candidate to the set without comparing the motion vector prediction candidate with other motion vector prediction candidates already included in the set; and selecting one motion vector prediction candidate from the set to represent a motion vector prediction for the block of pixels.
 24. The non-transitory machine-readable medium according to claim 23, wherein said comparing comprises at least one of the following: comparing a reference index of the motion vector prediction candidate with a reference index of the at least one spatial motion vector already included in the set; and examining whether the motion vector prediction candidate is generated by processing one or more than one motion vector prediction candidates or not.
 25. The non-transitory machine-readable medium according to claim 23, wherein the temporal motion vector prediction is based on motion vectors of co-located blocks of a current frame and a previously encoded frame. 